This invention relates to a semiconductor laser device including a semiconductor laser element with an exit surface from which laser radiation can emerge and a collimating lens means which can reduce the divergence of the laser radiation emerging from the exit surface at least with respect to the first direction, which is perpendicular to the exit direction of the laser radiation. Furthermore, this invention relates to a semiconductor laser module for one such semiconductor laser device and a process for producing one such semiconductor laser device.
International patent application WO 02/082164 A2 discloses a semiconductor laser device and a process of the aforementioned type. The semiconductor laser device includes a semiconductor laser element which can be soldered onto a heat sink. The semiconductor laser element described therein, is a so-called laser diode bar which has line emission surfaces which are located in one direction spaced apart from one another and which extend lengthwise in this direction. In front of the outlet surface of the semiconductor laser element, there is a collimating lens means which is made as a fast axis collimating lens, in the case of the laser diode bar. This fast axis collimating lens reduces the divergence of the laser radiation in the direction perpendicular to the direction in which the line emission surfaces are located next to one another. This direction is called the fast axis. The laser radiation which has been collimated in this way in the direction of the fast axis can be further collimated in the direction perpendicular thereto, the slow axis, and can be focused onto a glass fiber.
The fact that the heat sink is a large copper block, but the semiconductor laser element is a diode of gallium arsenide, is a problem in these semiconductor laser elements. Gallium arsenide and copper have distinctly different coefficients of thermal expansion. For this reason, the solder layer between the heat sink and the semiconductor laser element may not be made very thin, and may not be implemented at very high temperatures because in both cases thermally induced stress would occur which is so high that the semiconductor laser element could be damaged. The solder layer conventionally has a thickness of roughly 5 microns and is produced at temperatures between 180° C. and 200° C. It is therefore a comparatively soft solder layer. In particular, as a result of this soft solder layer, however also for example with alternative attachment methods such as screwing the semiconductor laser element onto the heat sink, bending of the semiconductor laser element can occur over the length of its emission surfaces or its exit surface. This bending is generally called “smile” distortion. Laser radiation with “smile” distortion which passes through a fast axis collimating lens is deflected up in the middle area in which the exit surface is shifted down relative to the outer areas in this middle area. In this way, in the art, laser radiation arises which emerges from the collimating lens means, which runs apart in the direction of the fast axis and which is thus difficult to further process. In the semiconductor laser devices, known from the art, this leads to large intensity losses of the laser radiation which emerges from the semiconductor laser device. In the aforementioned art, the attempt is made with comparatively complex means to compensate for this “smile” distortion. To do this, many different lens means are used which are tilted to one another and which are located next to one another.
The object of this invention is to devise a semiconductor laser device of the initially mentioned type in which these distortions can be avoided with simple means. Furthermore, a semiconductor laser module for one such semiconductor laser device will be devised. Furthermore, a process for producing one such semiconductor laser device will be given.